Where should the forms.py file be located?

I'm starting to write my first Django project right now and I need to make my forms.py file for an app. I've seen some tutorials store the file under the main folder for the project and some in the app directory.

1. Which layout is the best for me if I want to make a form that only applies to one app?

2. Is it suitable to make more than one file to keep my forms code in?

Thanks!